<!DOCTYPE HTML>
<html>
<head>
<meta name="viewport" content="initial-scale=1">
<title>WebGL Canvas Read Pixels And Tab Switch Test</title>
<style type="text/css">
.nomargin {
  margin: 0px auto;
}
</style>
<script>
let g_swapsBeforeAck = 15;
let g_canvas;
let g_gl;

function sendResult(status) {
  if (domAutomationController) {
    domAutomationController.send(status);
  } else {
    console.log(status);
  }
}

function waitForFinish() {
  if (g_swapsBeforeAck == 0) {
    sendResult("SUCCESS");
  } else {
    g_swapsBeforeAck--;
    window.requestAnimationFrame(waitForFinish);
  }
}

function handleVisibilityChange() {
  if (document.visibilityState == "visible") {
    waitForFinish();
  } else {
    // Read pixels will cause drawing buffer to be cleared, but it shouldn't
    // cause it to be recomposited after the tab switches back.
    let pixels = new Uint8Array(4);
    g_gl.readPixels(0, 0, 1, 1, g_gl.RGBA, g_gl.UNSIGNED_BYTE, pixels);
  }
}

function main() {
  document.addEventListener("visibilitychange", handleVisibilityChange, false);

  g_canvas = document.getElementById("c");
  g_gl = g_canvas.getContext("webgl");

  let width = g_canvas.width;
  let height = g_canvas.height;

  g_gl.enable(g_gl.SCISSOR_TEST);
  g_gl.scissor(0, 0, width, height);
  g_gl.clearColor(1, 0, 0, 1);
  g_gl.clear(g_gl.COLOR_BUFFER_BIT);

  g_gl.scissor(0, 0, width / 2, height / 2);
  g_gl.clearColor(0, 1, 0, 1);
  g_gl.clear(g_gl.COLOR_BUFFER_BIT);

  g_gl.scissor(width / 2, height / 2, width / 2, height / 2);
  g_gl.clearColor(0, 0, 1, 1);
  g_gl.clear(g_gl.COLOR_BUFFER_BIT);

  sendResult("READY");
}
</script>
</head>
<body onload="main()" class="nomargin">
<canvas id="c" width="100" height="100" class="nomargin" style="background-color:black"></canvas>
</body>
</html>
